1. Field of the Invention
The present invention relates to a receiver receiving radio signals such as television signals by an antenna having an electrically switchable directivity and decoding the same as well as a receiver receiving radio signals such as television signals by space diversity or directivity diversity and decoding the same.
2. Description of the Background Art
Diversity, which switches characteristics of antennas, has been performed for receiving radio signals with high quality. This diversity includes spatial diversity, directivity diversity and others.
According to the space diversity, a plurality of antennas are arranged in spatially spaced positions, respectively, and the antenna actually receiving radio signals is switched among the plurality of antennas for receiving the radio signals. According to the directivity diversity, the plurality of antennas have different directivities, respectively, and the directivity is switched among them for receiving the radio signals.
According to the space diversity and directivity diversity, the antenna or directivity is switched when a quality of a received signal such as a strength of the received signal becomes lower than a threshold (see Makoto Taromaru and Yoshihiko Akaiwa, “A Theoretical Performance Analysis of Antenna Switch Diversity for TDMA Mobile Radio”, IEICE Trans., B-II, Vol. J80-B-II, No. 9, pp. 805-808, September 1997).
As an antenna having a switchable directivity, an antenna, which is formed of one feeder element and a plurality of passive elements equally spaced around the one feeder element, has been known. In this antenna, the directivity can be changed by changing sets of reactance values loaded in the plurality of passive elements. The antenna, of which directivity can be switched in accordance with the set of reactance values, is controlled to change the directivity in accordance with a strength of a received signal for receiving radio signals of higher intensities (see Takuma Sawaya, Kyoichi Iigusa and Takashi Ohira, “Basic Theory on 3-element Espar Antenna for Reactance Diversity Viewpoint”, Technical Report of IEICE, DSP2002-161, SAT2002-111, RCS2002-230, January 2003).